This invention relates to continuous presses in general and more particularly to an improved continuous press which includes side sealing means to permit the pressing of materials which would otherwise be forced out from between the forming spans in the press.
A continuous press which has two rotatably driven endless conveyor belts (forming bands) forming opposed substantially linear spans defining a pressing zone and which includes press platens applying pressure through the traveling spans to the work carried therebetween with antifriction rollers interposed between the platens and spans is disclosed in U.S. application Ser. Nos. 308,556 and 519,626. Such presses are useful for the continuous production of pressboard panels, panels of synthetic material and panels of other similar materials. In the aforementioned applications, the press is described in conjunction with the production of pressboard panels. However, by nature, such presses are also suitable for numerous other materials. However, when applied to certain materials, a situation may exists in which the material being pressed would be squeezed out from the linear spans. Such does not happen in the case of making pressboard from a mixture of wood chips. However, when soft viscous paste-like material are treated under very high pressure and heat, they can be forced out at the side edges of the belt loops or forming bands. Such occurs, for example, when a press of this nature is used to produce panels made of chips or shavings of thermoplastic synthetic materials which become soft during the pressing process in order to effect a bonding of the entire mixture. Such materials will be squeezed out at the edges since the thermoplastic mass has become plastic during the treatment. As a result, perfect panels can be made because the required pressure will not be built up within the mass, the pressure being released by the squeezing out.
There have been experiments performed in which stationary steel strips have been disposed at the edges of the conveyor belts. These have been used in an attempt to obtain an enclosed pressure space such as the type of obtained in multilayer hydraulic presses. However, the experiments did not yield satisfactory results. Aside from the serious problems of friction, sealing could not be obtained at the high pressures being used. Thus, the need for an effective manner of using such presses with plastic materials which will normally be squeezed out is evident.